Guidewires are used in a variety of medical applications including intravascular, gastrointestinal, and urological. For example, a common vascular application is Percutaneous Transluminal Coronary Angioplasty (PTCA). This procedure can involve inserting a guidewire through an incision in the femoral artery near the groin, advancing the guidewire over the aortic arch, into a coronary artery, and across a lesion to be treated in the heart. Similarly, angioplasty performed in other parts of the anatomy is called Percutaneous Transluminal Angioplasty (PTA) and may also involve the use of a guidewire. Typical vascular guidewires are about 50 cm to 300 cm in length, and are about 0.010-0.038 inches in diameter depending upon the application.
Common gastrointestinal uses of guidewires include endoscopic procedures in which an endoscope may be inserted into the mouth and advanced through the esophagus to the bile duct, the cystic duct, or the pancreatic duct. A guidewire is then threaded through a lumen in the endoscope and into the bile duct, cystic duct, or pancreatic duct. For purposes of this disclosure, “distal” refers to the end further from the device operator during use and “proximal” refers to the end closer to the device operator during use. Once the distal tip of the guidewire is located in a position desired to be treated, a diagnostic or therapeutic medical instrument is advanced over the guidewire and to the treatment area. The guidewire and the instrument may then be observed through the endoscope as treatment occurs.
Urological uses of guidewires include the placement of ureteral stents, or the placement of a basket-type retrieval device to retrieve kidney stones. Ureteral stenting, for example, is required when the normal flow of urine from the kidney into the bladder is compromised perhaps by tumor growth, stricture, or stones. Generally, the procedure involves the insertion of a ureteroscope through the urethra and into the bladder. A guidewire is then advanced through the ureteroscope and into a ureter. The wire is then forced through the compromised portion of the ureter. Once the guide wire is in place, a ureteral stent is advanced over the guidewire and into position in the ureter. The guidewire may then be removed and the stent will maintain the patency of the fluid path between the kidney and the bladder. The procedures described above are but a few of the known uses for guidewires.
Pushability, kink resistance, torqueability, and bendability are closely related and important features of a guidewire. It is important that force applied at the proximal end of a guidewire is transferred to the distal end of the guidewire. In addition, a guidewire must exhibit good bendability. This characteristic is a balance between adequate flexibility to navigate a tortuous lumen and suitable rigidity to support tracking of another device such as a catheter. Torqueability is closely related to the torsional rigidity of the wire and is ultimately demonstrated by how well rotation imparted to the proximal end of the guidewire is translated to the distal end of the guidewire.
Kink resistance is also an important characteristic of a guidewire. Kink resistance is closely related to the stiffness of the wire. Very stiff wires often provide good pushability (axial rigidity) but poor kink resistance. Kink resistance is measured by the ability of the guidewire to be forced into a relatively tight bend radius without permanently deforming the wire. A kink can lead to an improper force transfer and pushability along the guide wire.
Many guidewires exhibit a transition in stiffness along their length from a relatively more stiff portion in the proximal end to a relatively less stiff portion in the distal end. This provides a more desirable combination of pushability and the ability to navigate tortuous vessels. For some applications, the preferred transition is a smooth and continuous transition from stiffer to less stiff.
Several different types of guidewires are well known in the art. One type of known wire is characterized by a solid metal core surrounded by a metal coil. Typical metals for the core may include spring steels and stainless steels. Coils are usually made of the same variety of metals used as core materials. The coil is usually made of round wire or flat wire and surrounds either the entire length of the core or only a portion of the core. The coil usually is formed by helically wrapping the wire around a mandrel, removing the mandrel, and inserting the core into the coil. The pitch of the wire coil may be varied along the length of the coil to vary the stiffness of the coil. Changes in the pitch of the coil can result in flexibility changes to the resulting guidewire structure.
Traditional coil over core wires also achieve a transition in stiffness along their length by using a ground core. In current guidewire technology, for example, the distal tip of the core is usually ground to a taper to provide the characteristics of added flexibility near the tip. In the above described examples, the core wire portion of the guidewire is formed from a base cylindrical metal stock material that is then machined down to a predetermined profile and cross-sectional configuration.
The stock material used for guidewire construction is usually a continuous length of cylindrical wire cut to a desired length after machining. The cylindrical stock material is machined along certain portions to obtain a desired outer diameter to control flexibility. The grinding required to alter the device's flexibility is usually accomplished with a particular manufacturing machine tool called a center-less grinder. Often using a rotating cutting wheel/blade, a center-less grinder cuts away portions of the stock material profile to attain a precise desired configuration. For example, a known centerless grinder machine tool is described in U.S. Pat. No. 5,674,106, the entire contents of which are hereby incorporated by reference.
The use of a center-less grinder machine has a number of undesirable drawbacks related to the manufacture of guidewires. For example, the operation of a center-less grinding machine is a labor intensive procedure that requires an experienced operator. In addition, the process results in a relatively high scrap rate, resulting in excess material cost. Moreover, center-less grinding stations, including the actual machinery and related components, leave a large footprint occupying valuable and costly production space otherwise available for alternative uses. Despite these drawbacks, and since guidewire flexibility is largely determined based on the resulting machined profile of the base core wire, dependable alternative configurations and methods of manufacture have, as of yet, not been successful.
The profile and cross-sectional configurations of guidewires formed with a center-less grinding machine inherently results in distinct portions having a smooth or tapered cylindrical outer diameter. The inherent cylindrical configuration results in a number of characteristics that hinder the desired performance of such guidewires during use. For example, the outer diameter of the guidewire, even with a fluoropolymer coating, can result in undesired friction during movement within a working channel of an endoscope. The friction results from contact between a relatively large portion of the exterior perimeter of the guidewire against an internal surface of a working channel in an endoscope.
In addition, the inherent cylindrical geometry resulting from center-less grinding also occupies valuable area within the working channel of an endoscope. For example, the necessary area occupied by the inherent geometry of such guidewires limits potential for increased fluid flow within a working channel during irrigation and suction. In addition, the shape of such guidewires can reduce the capability for alternate device passage resulting from potentially unoccupied additional working channel space available with alternative guidewire geometries.
Accordingly, there is a need for alternative guidewire configurations and methods of manufacture that result in guidewires exhibiting the features of pushability, kink resistance, torqueability, and bendability.